The broad objective ofthis researchproposal is to obtain insights into the processes which control the synthesis and, degradaton (renewal), and the assembly of cardiac intracellular proteins and organelles. We wish to evaluate the participaton of changes in transcription of individual messenger RNAs in the abrupt stimulation, or inhibition of protein synthesis which occurs during the experimental development or regression of cardiac hypertrophy. We will evaluate the role of changes in the relative cncentratons of tRNA isoaccepting species, and in the level of their changing with amino acids in the control of synthesis and degradation ofmyofibrillar proteins. We will also study compartmentalization of the amino acid precursor pool in heart muscle wth the aim of characterizing the process of reutilization, of amino acids derived from protein degradation, for protein synthesis. We wll directly compare the secific activities of aminoacyl tRNA, total free intracellular amino acid and extracellular amino acid pools during periods of rapid protein synthesis and degradation, to determine if there is a preferential shunting of amino acids derived from protein degradation intothe aminoacyl tRNA pool. The possibility of non-random assembly andturnover of myofibrillar proteins wll be evaluated. We also plan to study changes in RNA transcription, protein translation andthe proliferative response of cardiac mitochondria, tostimuli that lead to the rapid accumulaton or removal of mitochondria.